1. Field of the Invention
The present invention relates to a keeper of a dental magnetic attachment that fixes a denture by using magnetic attractive force.
2. Discussion of the Background
A dental magnetic attachment that fixes a denture by using magnetic attractive force has already been developed in the dental field. The prior dental magnetic attachment 9, as shown in FIG. 3, comprises a magnetic assembly 91 embedded in a denture 81 and a keeper 92 embedded in a root cap 82 to contact the magnetic assembly 91. The keeper 92 is made of soft magnetic material that generates attractive force between the keeper 92 and the magnetic assembly 91.
The dental magnetic attachment in this structure requires the condition that the keeper 92 is cast in the root cap 82. The casting process in which the keeper 92 is incorporated into the root cap 82 requires precise control of casting conditions at an elevated temperature to maintain the good quality of the keeper 92. The process requires a lot of time and is prone to various problems. As the result, the cost of keeper preparation is increased significantly. It also prolongs the medical treatment period for the patient.
Therefore, recently, a keeper is cemented directly on the tooth root surface using advanced dental resin that has been developed. This type of keeper 92, as is shown in FIG. 4, comprises a keeper body 921 and a root 922 which are linked together by welding. (cf. Unexamined patent application publication 2000-137260)
However, the keeper 92 mentioned above faces the following difficulties.
As mentioned above, in the keeper 92, the keeper body 921 and the root 922 are connected by welding. The root 922 is sometimes referred to as a post. Therefore the welding process, which takes a lot of time and labor, makes it difficult to decrease the cost of the keeper. The welded structure itself has no special problem in strength, but because of the nature of welding, it is not possible to overcompensate very much on weld strength so there is not much leeway when it comes to strength. So the strength of the border between the keeper body and the root part, that is, the strength of the keeper has been required to be elevated.
The prior keeper 92, as is shown in FIG. 4, has an excellent structure that has a smaller diameter bendable part 923 and that enables the root 922 to be bendable. Moreover, a step part between the bendable part 923 and larger diameter taper part 924 prevents embedded keeper 92 from coming off.
But the step part is not enough to prevent the keeper 92 from coming off and more excellent structure to prevent coming off has been required.